Colon cancer is the second leading cause of cancer mortality among adult Americans, accounting for 150,000 new cases and 70,000 deaths annually in the U.S. population. Each American carries a 7% lifetime risk of developing colon cancer. An essential feature of colon cancer, which carries the promise that colon cancer can be prevented in the population, is that colon cancer arises from a precursor, the adenomatous colon polyp. The aim of this pilot project is to identify and to collect blood from the 300 sib pairs in which both sibs are known to have in the present or the past to have developed a colon neoplasm (either an adenomatous colon polyp or a colon cancer) and to perform a linkage study to identify one or more major genes that predispose to the formation of colon polyps, and hence the existence of colon adenoma susceptibility allele.